A Los Angeles County sheriff's deputy alerts a resident of mandatory evacuations on January 8th, 2018, in the Creek Fire burn area.

(Photo: Los Angeles County Sheriff's Office)

Last month, a huge swath of Southern California was on fire. Now, with heavy rain imminent, local residents are holding their breath in anticipation of what might happen next.

Officials in Santa Barbara, Ventura, and Los Angeles counties have instituted mandatoryevacuations in anticipation of the latest weather calamity in a besieged stretch of the state. The same residents that were, until recently, blanketed with wildfire smoke are now filling sandbags to prepare for a flood.

Nearly double the normal rainfall for the entire month of January—up to 10 inches on ocean-facing mountain slopes—is expected to fall in a matter of hours on Monday night into Tuesday morning. Los Angeles, which received less than an inch of rain between March 1st, 2017, and January 1st, 2018, could get three times that in less than a day. The worry is that the ground, having just been singed by flames, will be unable to sop up the excess moisture, directing damaging mudslides toward the very same communities still in recovery from the fire.

On Monday, Meteorologists raised their highest alert for excessive rainfall as a major Pacific storm is set to take aim—coincidentally—on the exact same stretch of coastal real estate that was ravaged in the Thomas Fire, the largest wildfire in state history.

"In some spots, fire burned with such extreme intensity that it incinerated all vegetation and 'cooked' the soil underneath," University of California–Los Angeles climate scientist Daniel Swain tells Pacific Standard. "It's those really high-intensity burn patches, plus those occurring on steep slopes, that will have the greatest potential for debris flows and flash flooding."

The term "debris flow" seems relatively mild for what is now "a near certainty," in the minds of weather forecasters: Ash, soil, rocks, and charred trees have become untethered to the land, with no grasses or small shrubs to hold them in place. On top of that, add in rainfall in hurricane-like quantity and intensity, and whole hillsides could give way in a swirling torrent of Earth, rushing downhill with a consistency much like wet cement.

If that description sounds dramatized, consider that, in California, the past few weeks of weather read more like a Hollywood script than real life. Raindrops are falling across Southern California for the first time in more than 300 days. During that period, the driest on record for some locations, the massive Thomas Fire exploded in size during an unrelenting mid-winter period of strong winds. Now, a massive rainstorm arrives, almost perfectly placed to inflict maximum damage.

The 2017 wildfire season, the worst in the United States' history, was three times as costly as the previously most destructive year. Whatever damage occurs this week will be treated as a separate, though linked, disaster. With any luck, there will be a lull that will allow residents, and the rest of us, to consider how to radically rethink our response to reduce the effects of the disasters still to come.